Preheat the oven to 350°F (175°C). Grease and flour three 8-inch round cake pans.
In a medium bowl, whisk together all-purpose flour and baking powder; set aside.
In a large bowl, cream the unsalted butter and granulated sugar together until light and fluffy.
Add eggs one at a time, beating well after each addition.
Alternately add the dry ingredients and whole milk to the butter mixture, starting and ending with the dry ingredients. Mix until just combined.
Stir in vanilla extract.
Divide batter evenly among the prepared pans.
Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
Allow cakes to cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
For the vanilla buttercream frosting, beat together powdered sugar and unsalted butter until smooth.
Add heavy cream and vanilla extract, and beat until light and creamy.
Divide the frosting into three portions. Tint one with pastel pink, one with pastel blue, and leave one white.
Place the first cake layer on a cake stand or plate. Spread a layer of white frosting evenly on top.
Repeat with the second layer, using pastel pink frosting, then top with the third layer and cover the entire cake with pastel blue frosting, smoothing the surface.
Pipe rosettes around the edges using the tinted frostings for decoration.
Add edible gold glitter sparingly over the top for a shimmering effect.
Finish by placing the fondant number ’18’ topper centered on the top tier.